On Kanye West“I started out as his keyboard player. People don’t realize how calm he is. He may be passionate and have these great rants that everybody loves, but behind the rants is a steady train. When we were in Hawaii for months [recording 2010’s My Beautiful Dark Twisted Fantasy], we’d just be there and work. It’s not like the life of a superstar, eating caviar, rolling out of bed whenever you want. He’s up at 6 a.m. sending emails, ready to go play basketball, stay in shape, get in the right frame of mind. A lot of people know how to make an album, but [he’s like,] ‘How do I make the best album I’ve ever made again?’ Especially after you’ve done it, like, five times.”Key tracks: ”Monster,” ”All of the Lights,” ”Love Lockdown”

On Taylor Swift “She’s very hands-on and in control of what she’s doing. She came to my little studio in Venice by herself with no entourage and said, ‘Hey, thanks for meeting with me, I’ve got this song I’d love you to produce. Here it is.’ And she sat down on my couch and sang it for me and said, ‘What do you think?’ There’s no smoke and mirrors or fluke or trendiness going on here — this is music she writes from her experiences. I’ll give you an idea of how tough this girl is: It was a summer day, and sometimes I turn the air-conditioning off in my vocal booth so it won’t make noise while we’re recording. And I had kind of forgotten about that. It was hotboxed in there. I almost sent Taylor Swift to the hospital for dehydration! [Laughs] I was mortified. But she did not complain.”Key tracks: ”Holy Ground,” ”The Lucky One”

On Bruno Mars“We kind of came up in the game together. And to his credit, becoming the superstar that he is, he has not changed one bit. He really encourages me to be hard on him. He brought a few of us in to bring different points of view [to 2012’s Unorthodox Jukebox], and I think it shows. ‘Locked Out of Heaven’ is a vastly different record from ‘Just the Way You Are’ or ‘Gorilla.’” Key tracks: ”Locked Out of Heaven,” ”Gorilla”

On fun. “I was working with Beyoncé, and I was like, ‘What am I going to do with this rock band?’ But they’d been listening to a lot of urban music and noticed that my name kept popping up in the credits, so they’d decided that they were open to what I did, and gave me pretty much full rein. Every time I’d think, ‘Maybe this is too out of their comfort zone,’ they’d be like, ‘No, give us more! Go further!’ [2012’s Some Nights] was kind of a reverse Kanye. Kanye brings elements from unsuspecting places into the rap world; they were like, ‘We’re an indie-alternative band, and we want to bring this tough hip-hop element into what we do.’” Key tracks: ”We Are Young,” ”Some Nights,” ”Carry On”